1. Field of the Invention
This invention relates to a process for thermally bonding non-woven materials comprised of two-component melt blends wherein the thermal bonding is achieved at temperatures appreciably lower than the bonding temperature of the lower melting component. More specifically, this invention relates to the process for thermally bonding mixtures of polyesters with terpolymers comprising lactams, polyols and polyacyl lactams at temperatures below the bonding temperature of the individual component polymers. This has been found to result in the composite article such as non-woven fabric having a bonded strength greater than fabrics resulting from, for example, the polyester or the terpolymer bonded individually at the same temperature. In yet another aspect, the invention relates to a thermally bonded non-woven fabric comprised of melt blended fibers of polyester and the said terpolymers.
2. Description of the Prior Art
The fibers comprising a non-woven fabric have in the past been bonded by the use of external binders or by softening the fibers with heat, solvent or plasticizer and subjecting them to pressure while in the softened state. The external binder may be an adhesive substance which is cured after the application thereof or it may be rendered adhesive after application by use of heat, solvent or plasticizer. External binders may be applied as powders, solutions, or emulsions; however, these methods suffer from several disadvantages. The use of an external binder presents problems in uniform application and limits the properties of the entire web to those of the binder. Thus, for example, if an adhesive with a relatively low melting point is used as a bonding material, the temperature conditions to which the web or resulting fabric may be subjected are limited by the melting point of the adhesive.
Solvent bonding by the previous methods is not easily controlled and frequently tends to alter the aesthetic properties of the web. For example, achieving adequate adhesion between the filaments without dissolving the entire web or at least impairing the physical properties thereof is difficult. Furthermore, the intersections at which the filaments are bonded frequently have a swollen appearance which evidences the solution and redeposition of polymer. In most instances, these swollen areas around the bonds do not possess the same dye acceptance level because of changes in the crystalline structure which is localized at the bond site thereby causing non-uniform dyeing.